This invention relates to gas turbine engines and, more particularly, to thrust vectorable nozzles for use therein.
The high velocity imparted to the exhaust gases of a gas turbine engine by the exhaust nozzle provides the thrust for propulsion. This thrust is substantially parallel with, and opposite to the direction of, exhaust gases exiting the nozzle. Consequently, if the direction of the exhaust gases is changed, the direction of propulsive thrust is correspondingly varied. Typically, aircraft gas turbine engines are provided with nozzles which are fixed in the axial direction, and aircraft maneuvering is accomplished solely by airframe control surfaces.
Advanced aircraft configurations contemplate, and may even require, the selective redirection (or vectoring) of gas turbine engine thrust in order to enhance aircraft performance and to provide the aircraft with operational characteristics heretofore deemed impractical. For example, if the exhaust of a conventionally installed gas turbine engine was directed downward, rather than rearward, to a direction substantially perpendicular to the engine longitudinal axis, the resulting upward thrust would provide direct lift for the aircraft and, therefore, a vertical take-off and landing capability. Similarly, thrust vectoring during flight can greatly increase aircraft maneuverability since the thrust force can augment the manuevering forces of the aircraft control surfaces such as elevators, ailerons and rudders. In order to accomplish such thrust vectoring, a device is required to efficiently and practically alter the direction of gas turbine engine exhaust nozzle gases.
The concept of thrust vectoring by itself is not new since exhaust nozzles with this capability have been considered for years, and a wide variety of thrust vectorable nozzles have evolved. However, these nozzles have typically included one or more of the following limitations:
Discontinuous vectoring between the cruise mode and the lift mode; PA1 Air frame doors required to accommodate exhaust deflectors in at least one operational mode; PA1 low lift thrust available when compared to the required weight addition of the basic cruise engine; PA1 excessive complexity; PA1 excessive downward projection in the lift mode resulting in ground clearance problems; and PA1 slow vector angle and nozzle area rate of variation.
The problem facing the gas turbine engine designer, therefore, is to provide a flight maneuverable exhaust nozzle which avoids all of the above limitations.